1. Field of the Invention
The present invention relates to a trichromatic colorimeter by which chromaticity coordinates (x and y) of the CIE standard are obtained.
2. Description of the Prior Art
The prior art trichromatic colorimeter obtains the CIE chromaticity coordinates (x and y) using 3 or 4 sets of filters and photosensitive elements, which obtain X, Y and Z represented by equation (1) below: ##EQU1##
The X, Y and Z are obtained using a linear light measuring circuit, and are then applied as inputs to an operation circuit. The x and y are finally obtained by the operation of equation (2) below: ##EQU2##
It should be noted that P.sub..lambda. represents a relative spectral distribution of a light source, .rho..sub..lambda., the spectral reflectance for an object to be measured, and x.sub..lambda., y.sub..lambda. and z.sub..lambda., the spectral tristimulus values of the CIE standard colorimetric observer in equations (1) and (2) above. The x.sub..lambda., y.sub..lambda. and z.sub..lambda. have their own characteristics as shown in FIG. 1. It is also noted that .rho..sub..lambda. is equal to 1 (.rho..sub..lambda. =1) when a light source color is an object to be measured.
When a linear light measuring circuit is used for the above light measuring device, a high power voltage is required to widen a measuring range. Also, this poses a problem of low measuring accuracy.